Particulate heating/cooling agents

ABSTRACT

This invention discloses novel compositions of matter, in particulate forms, which function as heat transfer agents for heating or cooling applications. The particulates comprise solid carriers containing microwave responsive substances which are liquid at a predetermined elevated operating temperature. These particulate agents, preheated by microwave energy, serve as sources of dry heat or moist heat, depending on their composition. They also serve as sources of cold, when prechilled in a freezer.

This application is a division, of application Ser. No. 07/797,403,filed Nov. 25, 1991, now U.S. Pat. No. 5,314,005 issued May 24, 1994.

BACKGROUND OF THE INVENTION

1. Technical Field

This invention concerns materials which can serve as intermediate agentsfor transfer of heat from an energy source to a load object. Morespecifically, it relates to particulate compositions of matter which canbe used effectively for heating or cooling applications.

In a typical heating application, agent B receives heat from source Aand delivers its heat to load object C. The same applies, in principle,to a cooling application. In that case, agent B receives cold (gives upits heat to) source A and gives up its cold (receives heat from) loadobject C. Putting it in another way, one may consider the load object ofcold as a source of heat and the source of cold as the load object ofheat. Thus, intermediate agents play a similar role in heating andcooling.

2. Description of Prior Art

Examples of common heating and cooling applications come to mind quitereadily. Electric corn poppers or hairdryers use air as the intermediateheating agent. Pressing irons or frying pans use metal as intermediateheating agents. Hot oil is used as an intermediate heating agent in deepfrying and water is used as the primary intermediate heating agent inmost cooking applications. Turning to a common example of cooling, airis the primary cooling intermediate in a refrigerator. All of the aboveare instances of dynamic, steady-state heat transfer, where theintermediate agents receive and discharge heat concurrently, eitherintermittently or continuously. Under these conditions, the agents'ability to transfer heat is of primary importance.

In other situations, the process of heat transfer is sequential ratherthan concurrent. In such cases, an intermediate heating (cooling) agentreceives heat (cold) from a source, stores the heat (cold) for later useand then delivers it to a load object, likely at another location awayfrom the original source. Sequential heating is exemplified by preheatedwater in a jacketed baby feeding dish or in a hot water bottle. Afreezer pack is an example of stored cold. It is clear that insequential heating/cooling applications the intermediate agents' abilityto store heat is an important attribute. Measures of capacity to storeheat for materials which do not undergo a change of state relate tospecific heat per unit weight and, in combination with density, specificheat per unit volume. Changes of state will be considered later.

One other attribute worthy of mention is fluidity; i.e. the agents'ability to flow readily and surround the load object, thereby deliveringheat to more than one surface. It can, and often does, play an importantrole in concurrent as well as sequential schemes of heat transfer, aswill become more evident in the discussion which follows.

Against this background, one can assess the ability of variousmaterials, in their respective physical states, to act as intermediateheat transfer agents.

Gases

Air and combination gases are readily available, and their fluidity isclearly an advantage. They are well-suited for heating applications, butrelatively slow and energy wasteful, unless the rate of heat transfer toload objects is enhanced by convection. The low specific heat and lowdensity of gases rule them out as agents for storage of heat, exceptwhere massive volumes of gas can effectively be employed. The samegenerally applies to cooling.

Solids

Metals are effective agents for transfer of heat by virtue of their highconductivity. However, low specific heat (approx. 0.1 cal/g° C.) andhigh density make them relatively poor agents for storage of heat,except when substantial mass can be brought into play. Inorganic,mineral-type solids are poor thermal conductors, largely unsuitable forheat transfer. Their moderate specific heat (0.2-0.3 cal/g° C.) is notsufficient for storage of heat or cold. Moreover, lacking fluidity,their mode of heat transfer is characteristically unidirectional andmost effective via immediate contact.

Liquids

Because of their physical attributes, liquids are uniquely suited formost heating and cooling applications. They possess fluidity and abilityto transmit heat by conduction as well as convection. Moreover, theirmedium density (0.8-1.2 g/cc) and high specific heat (0.5-1.0 cal/g° C.)make them ideal for storage of heat in sequential processes. A commonliquid such as water can also exist in other states, thereby extendingits effective range of operating temperatures. Water can exist as steamfor heating applications, with the full benefit of fluidity. It also canexist as ice for cooling applications, albeit at the expense offluidity. Changes of state enhance the ability of water to store andcarry heat by virtue of the latent heat of condensing steam (forheating) and melting ice (for cooling), over and above what is availablevia sensible heat solely in the liquid state.

Focusing our attention on sequential heating scenarios, i.e. thoseinvolving transfer of stored heat from a source to a load object,liquids would clearly seam to be the preferred choice. Gases aer simplynot worthy of practical consideration for reasons already enumerated,based on their physical properties. Solids might similarly be by-passedfrom consideration due to their lack of fluidity and limitedheat-storage capacity.

Non-metallic solids are also as slow and difficult to preheat or precoolfor subsequent use, as they are slow to give up their heat or cold.However, it seemed that the rule of solids deserved furtherconsideration in the light of opportunities presented by newdevelopments in materials and technology.

It should be noted that liquids are not the panacea for allheating/cooling applications. Many common liquids, water included,cannot serve as permanent and reusable intermediate agents, because theyare volatile, subject to loss by evaporation and therefore in need offrequent replacement. Volatile liquids risk pressure build-up inhermetically sealed containers. Non-volatile liquids are, of course,safer. However, volatile or not, liquids must be effectively contained,secure against leakage as a result of physical or thermal damage tomaterials which contain them. Moreover, liquids (at a density of 1.0g/cc, or higher) may be too heavy for some applications.

In the field of health-care, for instance, where the load object inanimate, there are many portable hot or cold compresses to choose from.Several compresses contain liquids or gels which must be preheated orprecooled before use, as described in U.S. Pat. Nos. 3,885,403 and3,780,537. Others derive their thermal effects from physical phenomenasuch as solution or crystallization, as cited in U.S. Pat. Nos.3,874,504 and 4,462,224. With the advent of microwave technology,several of the newer compresses are claimed to be preheatable in anymicrowave oven. They apparently contain gelled or relatively volatileaqueous liquids which can be damaged to the point of leakage orotherwise rendered ineffective by repeated use or excessive preheating.Therefore, they require elaborate precautions and occasionalreconditioning. Heating/cooling pads often present surface temperatureextremes which upon direct contact with the skin may cause "burns", hotor cold. Hence, they must be shielded by extra insulation before use.With all that considered, it is clear that heating/cooling pads andother devices could benefit from a wider choice of materials which aresafer and simpler to use.

The idea of using particulate matter for heating or cooling applicationswas proposed in my previous U.S. Pat. No. 4,937,412. Further developmentof this concept, since that patent issued, have uncovered novelcombinations of materials with useful and unique properties.Accordingly, the object of this invention is to provide novelcompositions of particulate matter which can serve as intermediateagents for storage and transport of heat or cold with some of thebenefits of liquids but without the shortcomings of liquids or otherexisting materials. A further object of the invention is to make suchmaterials versatile enough in physical property and function to makethem suitable for a wide variety of applications.

SUMMARY OF THE INVENTION

The present invention identifies particulate compositions of matterwhich can serve as intermediate agents for storage and transport of heator cold from a source to a load object. Porous or hollow absorbentparticles are, respectively, impregnated or filled preferably withmicrowave responsive liquids which include relatively non-volatilecomponents. The loaded particles retain the liquids, affectively, bycapillary action and physical containment. The non-volatile component ofthe liquid make the resulting compositions permanent and reusableintermediate carriers of stored heat, following preheating by microwaveenergy, or cold, following prechilling in a freezer.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As indicated previously, mineral-based solids are normally notconsidered to be good agents for storage and transport of heat. Insummary, they possess low specific heat and medium density whichrestrict their capacity to store heat or cold. Their lack of fluidityalso limits their ability to transmit heat or cold to a load object.Fluidized beds are special situations where solids in particulate forms,with the added benefit of fluidity, act as intermediate agents of heattransfer between a fluidizing gas and a load object.

Solid matter in particulate forms exhibits the same particle density butlower bulk density than a coherent solid, due to the interstitial voidsbetween particles. If the particles are made porous or hollow with thesame base material, that further reduces their bulk density. The netresult is that an aggregate of such solids exhibits even lower specificheat per unit volume, and diminished ability to accept and transportheat; i.e. they are, in effect, thermal insulators.

While the above scenario seems to be most unfavorable for any likelyheat transfer agent, it does present unusual and hitherto unrecognizedopportunities for creating new combinations of materials with uniqueproperties. Let us consider what happens when porous or hollow solidsare impregnated with liquids. Their density, both particle and bulkdensity, increases. Their specific heat, per unit of weight and unitvolume, also increases by virtue of the contained liquids, since thelatter are higher in specific heat than the solids. Let us furtherstipulate that the liquids in question are in fact microwave responsiveliquids which include relatively non-volatile components. The particlesretain the liquids by capillary action or physical containment, andtheir lack of volatility makes the resulting compositions microwavepreheatable and also reusable sources of heat. Let us further assumethat one such non-volatile component is not only hydrophilic but in facthygroscopic. In addition, let it contain some dissolved water, typicallyand preferably at a concentration which is at equilibrium with ambienthumidity. The presence of water further increases the specific heat ofsuch a combination of materials. It also provides it with the capabilityto supply moisture when heated and to replenish moisture from ambientatmospheric sources when not in use.

The particulate compositions of this invention thus consist of solidcomponents which act as carriers for contained liquids. The resultingcompositions possess physical properties which are intermediate betweenthose of pure solid and pure liquid, but without the afore-mentioneddrawbacks of liquids. With the added benefit of fluidity, aggrogates ofparticulate solids are therefore more suitable intermediate agents forheating/cooling applications.

The solid component of the particulate matter may be any inert,thermally stable and, preferably, non-toxic material. It needs to beinert toward the liquid it contains and, in the interest of safety,thermally stable and non-toxic. Other properties of the solid depend onthe mechanism which will retain the liquid components. For liquidabsorption, the solid needs to be porous and highly absorbent, able toreceive and retain the liquid by capillary action. Examples of suchmaterials include activated alumina, activated silica, molecular sievesand the like. For liquid encapsulation, the solid must also be suitablefor making capsules, with the liquid retained inside physically. Anynumber of such materials, natural and man-made, are available for thatpurpose and known to those skilled in the art of encapsulation. Theexact nature and specific choice of "wall" materials will depend on theliquid they are intended to contain and conditions under which they areto be used. The size and shape of the particulate matter thus madeshould be small enough to present sufficient surface and points ofcontact for heat transfer but not so small as to be dusty and difficultto handle. It should also be smooth-surfaced to minimize abrasion andpromote fluidity. Preferred sizes are in the range of 1/32" to 1/8" orapproximately 20 mesh to 6 mesh in the U.S. Sieve Series.

The microwave responsive liquids which are used in this invention shouldposses low volatility: i.e. negligible vapor pressure at 25° C. andboiling points, at normal barometric pressure, well above 150° C. Theyshould also be stable at least up to the maximum temperature in whichthey are to be used. Among materials which meet such requirements, butnot excluding others, are: ethylene glycol and its polymers, propyleneglycol and its polymers, glycerol and its polymers and the like.Microwave susceptibility is also exhibited by chemical derivatives ofsuch compounds. Among them are: esters of acetic acid and longer chainaliphatic acids, and side chains derived from alcohols or polyethers.

Microwave responsive liquids vary greatly in their physical properties,depending on their chemistry. Liquids rich in hydroxyl or ether groupsexhibit high microwave susceptibility, complete water miscibility andextreme hygroscopicity. Compounds in this category (hydrophiles), suchas glycerol and polyethylene glycols, are clearly preferred for deliveryof moist heat. Other compounds, those high in molecular weight and morecomplex in structure, are less microwave susceptible, virtually waterimmiscible and in fact moisture repellent. Compounds in this category(hydrophobes), such as monoglycerides and acetylated monoglycerides, arepreferred for delivery of dry heat. Properties such as specific heat,specific gravity, viscosity and chemical stability also need to beconsidered and, occasionally, traded off. That provides the practitionerwith substantial latitude in selecting microwave responsive liquids,either individually or in compatible mixtures, to suit any specificapplication. It is clear that for cold application alone, the liquidscontained in the carrier solids need not be microwave responsive. Theymay be any liquids which, prechilled, can serve as a source of cold.

The preferred materials of this invention are non-toxic, and many are infact food grade materials. They do not pose any hazard in case ofaccidental misuse or even ingestion. As a general rule, it is advisableto restrict the amount of liquid relative to the host solid, so thatdifferences in thermal expansion between the materials do not result inthe expulsion of liquid out of the solid with changes in temperature. Itshould also be noted that liquid components of the particulates need notnecessarily be liquid at room temperature; i.e. at 25° C. for thepurpose of this invention. They may be solid semisolid or evensupercooled liquids at room temperature, but meltable at some elevatedtemperature for their proper disposition and usage as liquid susceptors.Latent heat inherent in changes of phase may in fact be of benefit insome applications.

Operating temperatures of the particulate matter of this invention maybe as low as 0° F. (-18° C.); i.e. typical household freezer, which maybe used for prechilling an aggregate of particulate matter for a coldapplication. For heating purposes, aggregates of particulate matter maybe preheated up to practical limits of volatility and/or stability ofthe components in question. Clearly, heat application to animate objectsrequires, for the sake of safety, lower temperature than what istolerable for inanimate application. In either case, the temperature inthe core of a particulate aggregate, loosely packed, may besubstantially higher than at its outer boundary. Temperature gradients,core to surfaces, are inherent in the process of heat propagationthrough beds of particulate solids. That may be an advantage in heatingapplications for animate objects. As the bed cools down, it may in factbe possible to bring more heat to the outer boundary by mixing thecontents of the bed. The upper reaches of operating temperature areestablished as a matter of dynamic balance between heat generated, heatstored and heat either given up to a load object or lost to thesurroundings. Similar considerations applies to cold applications.

As stated previously, the type of heat delivered to a load objectdepends on the liquid which is contained in the particulate matter.Moist heat can best be delivered by hygroscopic liquids which arecontained in porous solids or vapor permeable capsules. Moisture givenup can later be restored by exposing the solid to ambient humidity. Dryheat may be delivered by solids containing liquids which are from ofmoisture; i.e. hydrophobic liquids, or hydrophilic liquids which arekept away from moisture in a moisture-free environment. The aboveoptions merely illustrate how similar results may be achieved by variouscombinations of materials and by the physical conditions of theparticulate agent and its environment.

The particulate compositions of this invention are uniquely situated forhealthcare applications. Heating/cooling pads comprising particulatematter in fabric bags, for example, have the following advantages.

a. Ability to deliver dry heat or moist heat, by specific choices ofliquid components.

b. Automatic recovery of moist heat capability from ambient air; i.e.without need for deliberate external resupply of water to replenishmoisture given up.

c. Relative lightweight compared to liquids, gels and most non-poroussolids.

d. Fast preheat (reheat) by microwave energy rather than conventionalmethods.

e. Repeated usage with minimal handling and preparation.

f. Dual functionality in one product; heat or cold.

g. Benefits from desirable properties of liquids; e.g. higher specificheat, without risk of leakage or drippy mess.

h. Good draping properties; never freezable to a solid mass.

i. Safer, gradual delivery of heat or cold, by the nature of heattransfer through static beds of solids.

Primary considerations has thus far been given to applications ofsequential heating; i.e. those entailing heat generation in themicrowave and later delivery of stored heat to a load object outside themicrowave. However, with the property of fluidity, particulate solids ofthis invention may be used as sources of heat inside the microwave. Anyobject which is inherently microwave transparent can be immersed in abed of such solids and be heated by them while the combination isundergoing microwaving. This and other aspects of the invention willbecome more evident from the examples which follow.

EXAMPLE 1

This is an example of a moist heating pad. A bag made of polyester felt,measuring about 10" by 4" inside, was filled with 11/2 lbs. ofparticulate matter, in 4 equal stitched compartments 21/2×4" each. Theparticulate matter consisted of beads of activated alumina 1/16" indiameter impregnated with a mixture of glycerol and water, the overallcomposition comprising 59% alumina, 29% glycerol and 12% water.Following microwaving for 3 minutes at 700 watts, the pad emittedperceptible moist heat, with a surface temperature 105° F. or greater,for 25-30 minutes.

EXAMPLE 2

This is an example of a cooling pad. Another pad, similarly sized andfilled with the particulate composition of Example 1 was fabricated as astitched bag with one surface made of polyester felt and the othersurface made of a thin polyester fabric. Following storage in thefreezer at 0° F. for 6 hours, the pad was applied to the inventor'sbody, with the thin polyester fabric directly on the skin. Skintemperature, measured by thermocouple, dropped from 85° F. to 56° F. in5 minutes. It dropped to 52° F. in another 5 minutes and then remainedat that temperature for the next 20 minutes.

EXAMPLE 3

This example demonstrates recovery of lost moisture. A facial compresswas made of fabric similar to Example 1 and filled with 12 ounces of thesame particulate composition. The compress was preheated at 700 wattsfor one minute and used by the inventor for a moist-heat facialtreatment for 20 minutes. A measurable drop in weight was noted afterthe single usage which was attributed to loss of moisture. The usedcompress was stored in the open, at a relative humidity of about 65%.About 75% of the lost weight was thus restored in 24 hours and 90% in 48hours.

EXAMPLE 4

This is an example of dry therapeutic heat treatment. Several pounds ofactivated alumina 1/16" diameter were impregnated with 65% by weight ofan acetylated monoglyceride. The overall composition of the particleswas 60% activated alumina and 40% acetylated monoglyceride. Theparticles were placed into a glass bowl and microwaved at 700 watts for4 minutes. Upon removal of the bowl from the microwave the inventorimmersed his bare hands into the particulate bed exercising and workingthrough the particles. Dry comforing heat was thus supplied to themuscle and joints for at least 15-20 minutes. Prolonged treatment waspossible at higher bed temperatures with the use of cotton gloves.

EXAMPLE 5

This example illustrates heating concurrent with microwaving. Theparticulates of Example 4 were returned to the microwave with aworkpiece of polypropylene material immersed in the bed. Thisthermoplastic material is not microwave responsive per se. Uponmicrowaving at 700 watts, in several steps of 4 minutes each, the bedbecame much too hot to touch. With the help of thermal gloves, it wasdetermined that the workpiece was soft and pliable; i.e. hot enough forreshaping. The workpiece was then reshaped, removed from the particulatebed and water-quenched, with its new shape retained.

EXAMPLE 6

This example illustrates the use of encapsulated liquid from acommercially available source. About 500 softgels (gelatin capsules.3/8" in diameter) containing cod liver oil, were filled into a4-compartmented bag made of thin polyester fabric. The bag was thenstored in the freezer overnight, where the oils in the capsules wasobserved to have solidified. Upon removal from the freezer, the bag wasapplied directly onto the skin of the inventor, with a towelsuperimposed and serving as outer insulation. The bag providedmoderately intense cold for about 15-20 minutes, with occasionalflipover of the bag or mixing of its contents. Based on experience withother particulate compositions, it is predicatble that smaller capsulesfilled with other materials would prolong the cold treatment.

The foregoing description is for the purpose of teaching the person ofordinary skill in the art how to practice the present invention. It isnot intended to detail all of those obvious variations and alternativeswhich will become apparent to the skilled practioner upon reading thedescription. It is intended, however, that all such variations andalternatives be included within the scope of the present invention whichis defined by the following claims.

What is claimed is:
 1. Particulate heating/cooling agents comprising:a)a carrier material which is solid, and b) a substance, retained by saidcarrier material, which is microwave responsive and liquid at apredetermined elevated operating temperature, said substance including aplurality of components, including water, which is a source ofreversible moisture, and a relatively non-volatile, hydrophilic andhygroscopic component, selected from the group consisting of polyhydriccompounds, polymers of polyhydric compounds and chemical derivatives ofeither.
 2. The particulate heating/cooling agents of claim 1, whereinsaid moisture is released by microwave heating and replenished fromambient sources upon cooldown.
 3. The particulate heating/cooling agentsof claim 2 wherein said ambient sources include humid air.